1. Field of the Invention
The present invention relates to a catalyst component for olefin polymerization and also to a process for producing polyolefins.
2. Description of the Background
The polymerization of olefins is accomplished by the aid of a catalyst generically called a Ziegler-type catalyst. In general, it consists of two components. One component is a transition metal compound and the second component is an organometallic compound. The transition metal compound is conventionally prepared by the use of a solid carrier such as magnesium chloride and magnesium dialkoxide. There has been a variety of related technologies.
The magnesium compound to be used as a solid carrier of the catalyst for olefin polymerization should have an optimum particle diameter so that the catalyst has an improved activity and the resulting polymer has a controlled particle diameter. To this end, the solid carrier is prepared by grounding a magnesium compound alone or in combination with an ester. The preparation of the solid carrier involves mechanical grinding as an essential procedure. Without this grinding procedure, the solid carrier does not contribute to the improved polymerization activity. Moreover, the solid carrier supports such a small amount of transition metal (.e.g., titanium) that the catalyst is poor in productivity per unit weight. Low productivity gives rise to a large amount of residual chlorine in the polymer and poses a problem associated with the particle shape and particle size distribution of the polymer. (Inadequate polymer particles cause troubles in polymer processing such as transfer line clogging with fine polymer powder.) Therefore, the grinding procedure is recognized as very important, and a great deal of works and expense have been spent to establish the best conditions for the grinding system (wet or dry), grinding machine, grinding intensity, and grinding time.
On the other hand, several methods proposed have been for the improvement of polymer morphology (particle diameter and shape). According to one method, magnesium is supported on an inorganic oxide such as silica. (See Japanese Patent Laid-open Nos. 291604/1986, 291105/1986, 119203/1987, and 119204/1987.) According to another method, a magnesium compound is dissolved in an alcohol or the like and then caused to separate out before being used as a carrier. (See Japanese Patent Laid-open Nos. 811/1981). These methods obviate the grinding process but require the complicated steps of supporting, dissolution, and separation, which have an adverse effect on the stable performance of the catalyst.
In view of the foregoing, the present inventors carried out research, which has led to the finding that a reaction product of metallic magnesium, an alcohol, and a specific amount of halogen has such a narrow particle size distribution that it can be used as such (without particle size adjustment by grinding) as a carrier of the catalyst for olefin polymerization. This carrier is comparable to or superior to conventional ones in ability to support titanium, polymerization activity, and stereoregulatory. In addition, not only does it give rise to a polymer having greatly improved morphology, but it also permits the control of polymer morphology if proper conditions are established for the reaction of metallic magnesium, alcohol, and halogen.
The carrier in the present invention is entirely different from any known magnesium-based carrier. It is a reaction product of metallic magnesium, an alcohol, and a specific amount of halogen. A method is known in which a small amount of iodine (or ethyl orthoformate) is added to the reaction of metallic magnesium with an alcohol. (See Japanese Patent Publication No. 7093/1971 and U.S. Pat. No. 3,657,361) In this process, however, iodine is used in a very small amount merely as a reaction initiator. By contrast, in the process according to the present invention, halogen is used in a much greater amount than is used as an initiator. This indicates that the reaction product in the present invention is entirely different from that disclosed in the prior art.
It is pointed out that in olefin polymerization using a Ziegler catalyst, slurry polymerization, solution polymerization, gas phase polymerization and the like are used for homopolymerization or copolymerization of ethylene. Of these, gas phase polymerization wherein polymerization is carried out substantially in the absence of liquid phase, is advantageous for ethylene polymerization since it does not require a large amount of solvent, leading to simplification of the process and cost effectiveness. Thus, the gas phase polymerization has been recently studied in ethylene polymerization using the Ziegler type catalyst.
However, in the case of using these magnesium compounds as a carrier material for a polymerization catalyst for olefins such as ethylene, it is necessary to use magnesium compounds having optimized particle size in order to improve catalyst activity and to control particle size of the resultant polymers. In this case, to control particle size, the magnesium compounds themselves are ground, or non-ground magnesium compounds are co-ground with esters when treated with the esters. In any case, a mechanical grinding, classification of the like is required.
When a carrier material which has not been subject to such grinding treatment, is used, the resultant catalysts have poor polymerization activity and the yield or productivity per unit catalyst decreases due to a small amount of transition metal (e.g., titanium) carried on a carrier. This causes a problem in that a large amount of chlorine may remain in the resultant polymers. Further, there may be a problem in that the resultant polymers may have undesirable shape and undesirable particle size distribution. Also, problems (e.g., clogging of transfer lines due to a large amount of micro-powders of the polymer generated) may occur during the process step of producing polyolefins such as an ethylene polymer.
Accordingly, the grinding step for the magnesium compounds is considered quite important. However, the mechanical grinding step requires much labor and costs even when only its condition determination is considered (e.g., a grinding system such as a wet type or dry type, grinding equipment, grinding strength, grinding time, which affect the shape of the ground products).
Further, in order to improve the morphology of the resultant polymers such as particle size and shape, several methods are known. Such methods include a method using magnesium carried on an inorganic oxide such as silica (Japanese Patent Application Unexamined Publication Nos. Sho 55-120,608; and 58-277,055); and a method using a product obtained by once dissolving a magnesium compound in a solvent such as alcohol and then again precipitating it (JP Pat. Appln. Unexamined Pub. No. 56-000,811). In these methods, the grinding step is not required. However, these methods require carrier treatment or dissolution/precipitation treatment resulting in extremely complicated steps and may give rise to poor stability of the catalyst performance.
Accordingly, it is desired to provide a method of controlling particle size, particle size distribution and shape of a carrier useful for an olefin polymerization catalyst, without using complicated procedures such as mechanical grinding and classification.
Further, as mentioned above, in particular, in the homopolymerization or copolymerization of ethylene using the Ziegler type catalyst, the gas phase polymerization wherein polymerization is carried out substantially in the absence of liquid phase, i.e., under gas phase conditions, has been recently studied. In the gas phase polymerization, controlling of shape of the resultant polymer particles is an important technical factor to prevent adhesion of the polymer particles to an inner wall of a reactor and clogging of transfer lines due to enlarged or agglomerated polymer particles, to stabilize the gas phase polymerization reaction.
On the other hand, pre-polymerization wherein a catalyst component is preliminarily treated with a small amount of olefin, has been attempted to keep the shape (particle size, particle size distribution) of the polymer particles at good level. For example, in Japanese published Patent Application No. Sho 55-029,512, it is proposed that a solid catalyst is preliminarily contacted with 1 to 500 grams of alpha-olefin per 1 gram of the catalyst. This technique has certain advantages. However, in this process, when hydrogen is used as molecular weight controlling agent, a problem which occurs is that the generation of micro-powders increases.
For this reason, in the gas phase polymerization of ethylene, it has heretofore been desired to provide a method capable of restricting generation of micro-powders even when hydrogen is used as molecular weight controlling agent, as well as capable of controlling particle size, particle size distribution and shape of a carrier useful for a polymerization catalyst, without using complicated procedures such as mechanical grinding and classification. Such method result in improvement of morphology, such as particle size, particle size distribution and shape, of the resultant polymer.
Further, a highly active catalyst has a problem in that when the catalyst as such is introduced into a polymerization reactor and exposed to high temperatures near polymerization temperature, the activity and the stereoregularity of the resultant polymer become insufficient, and the catalyst adheres to the reactor wall.
As a method of solving the above problems, a catalyst is subjected to polymerization treatment with a small amount of alpha-olefin. This is so called pre-polymerization. This pre-polymerization is usually performed in the slurry state with a diluting solvent in a stirring vessel.
However, if the amount of treatment for the pre-polymerization is increased, a problem which occurs is that the volume of the stirring vessel should be drastically increased, leading to poor cost performance of facilities. In addition, as a method of solving the disadvantages, an increase in slurry concentration has been considered. However, stirring cannot be sufficiently effected for highly concentrated slurries under the usual stirring conditions. Thus, catalyst performance decreases due to local heat generation, and the activity and the stereo-regularity of the resultant polymer become insufficient. On the other hand, when the slurry concentration is kept at a low level, a longer pre-polymerization time is required to obtain a prescribed amount of prepolymerization, resulting in a drastic decrease in activity.
It is desired to provide a method which is capable of performing pre-polymerization at high slurry concentration.
For this reason, in the production of polyolefins using a solid catalyst component, it has heretofore been desired to provide a method which is capable of performing pre-polymerization at high slurry concentration.
In view of these current situations, the present inventors have intensively studied the production of spherical catalyst carrier materials having controlled particle size and particle size distribution in one step reaction. As a result, it has been found that a solid product useful as a catalyst carrier material for olefin polymerization, having narrow particle size distribution, can be obtained by reacting metallic magnesium, alcohol and a specific amount of halogen and/or a halogen-containing compound, without using particle size control treatment such as grinding or classification. It has also been found that when olefin polymerization is carried out using an olefin polymerization catalyst component comprising the solid product as a carrier, the catalyst shows a titanium carrying ability and polymerization activity which are better or equivalent to those of a conventional catalyst, and the resultant polymers have drastically improved morphology and better or equivalent stereo-regularity to that of a contentional polymer. Further, the present inventors have found that the particle size of the resultant solid catalyst can be freely controlled by appropriately selecting the conditions for the reaction of metallic magnesium, alcohol and a halogen-containing compound.
Further, the present inventors have found that the generation of micro-powders of the polymer can be prevented even when hydrogen is used as a molecular weight controlling agent by way of a method of preparing a solid catalyst component for ethylene polymerization using, as a carrier, a solid product obtained by the reaction of the above metallic magnesium, alcohol and a specific amount of halogen and/or halogen-containing compound, further subjecting this material to a pre-polymerization treatment, and then subjecting the solid catalyst component to a contact treatment with at least one kind of gas selected from carbon monoxide and carbon dioxide, or a mixed gas of such gas and an inert gas. It has also been found that this method is particularly effective in gas phase polymerization.
Further, the present inventors have studied the preparation of polymers having improved morphology, particularly pre-polymerization at high slurry concentration. As a result, it has been found that effective pre-polymerization treatment can be performed even at high slurry concentration if a specific stirring wing and stirring conditions are used for pre-polymerization treatment using the solid catalyst component (A), when polyolefin is produced using the solid catalyst component (A).
Finally, thermoplastic elastomers are widely used, particularly as substitutes for vulcanized rubbers, as automobile parts, industrial machine parts, electronic or electric parts, building materials, and the like as energy saving or natural resource saving type elastomers.
Thermoplastic olefin elastomers (TPO) are generally manufactured by a process wherein polypropylene and ethylene-propylene-diene rubber (EPDM) are kneaded in the presence of a peroxide (e.g., Japanese Patent Laid-open (ko-kai) No. 217747/1986). The process, however, has drawbacks in that the procedure is complicated and the production cost is high.
On the other hand, a number of trials have been undertaken for the reduction of production costs by directly manufacturing at the polymerization step high molecular weight polymers having the same dynamic characteristics as those of the above-mentioned TPO. For example, propylene-hexane copolymers (e.g., Japanese Patent Laid-open (ko-kai) No. 53983/1974 and Japanese Patent Publication (ko-kai) No. 19444/1987), elastic polypropylene (Japanese Patent Laid-open (ko-kai) No. 179247/1986), and the like have been proposed.
However, all these high molecular weight polymers have insufficient low temperature characteristics. Although a propylene/ethylene-propylene two step polymerization method has been well known (e.g., Japanese Patent Laid-open (ko-kai) No. 50804/1982) as a method for improving the low temperature characteristics of polypropylene, it has been difficult to manufacture a vulcanized rubber-like polymer possessing both flexibility and a tension strength resistible for practical use by this method.